1. Field of the Invention
The invention relates to a new compound and a liquid crystal composition. More specifically, the invention relates to a liquid crystal compound having a five-membered ring, a liquid crystal composition including the compound and a liquid crystal display device containing the composition.
2. Related Art
A display device utilizing a liquid crystal compound has been widely used for the display of a clock, a calculator, a word processor or the like. The display device utilizes characteristics such as the refractive index anisotropy (Δn), the dielectric anisotropy (Δ∈) and so forth of the liquid crystal compound.
A liquid crystal phase includes a nematic liquid crystal phase, a smectic liquid crystal phase, a cholesteric liquid crystal phase, and the nematic phase is most widely applied. A display mode includes a DS (dynamic scattering) mode, a DAP (deformation of aligned phases) mode, a GH (guest-host) mode, a TN (twisted nematic) mode, a STN (super twisted nematic) mode, a TFT (a thin film transistor) mode, a VA (vertical alignment) mode, an IPS (in-plane switching) mode and a PSA (polymer sustained alignment) mode.
A liquid crystal compound used for these display modes is required to have a liquid crystal phase in a wide temperature range, centering at room temperature, a sufficient stability under conditions that the display device is used, and also sufficient characteristics for driving the display device. However, no single liquid crystal compounds that satisfy these conditions have been found until now.
The actual situation is that a liquid crystal composition is prepared by mixing from several to several tens of liquid crystal compounds in order to satisfy the required characteristics. It is required that the liquid crystal composition is stable to moisture, light, heat and air, which are normally present under conditions that the display device is used, and to an electric field or electromagnetic radiation, and also is stable chemically to a compound that will be mixed. It is required that the liquid crystal composition has suitable values of a variety of physical properties such as refractive index anisotropy (Δn) and dielectric anisotropy (Δ∈), depending on the display mode or the shape of the display device. Furthermore, it is important that each component in the liquid crystal composition has an excellent solubility in each other.
In recent years, modes such as IPS, VA and OCB among the display modes have been receiving attention as a display mode capable of overcoming a narrow viewing angle of a liquid crystal display device, which is the greatest subject to be solved. In particular, a liquid crystal display device having the VA mode or the IPS mode among liquid crystal display devices having these modes has been studied earnestly, since it has an excellent responsivity in addition to a wide viewing angle, and is capable of providing a high-contrast display. The liquid crystal composition used in the liquid crystal display devices having these display modes is characterized by the negative dielectric anisotropy (Δ∈). It is known that a liquid crystal composition having a large negative dielectric anisotropy (Δ∈) can decrease the driving voltage of a liquid crystal display device containing the liquid crystal composition. For example, see the none-patent document No. 1. Accordingly, liquid crystal compounds as the components of the liquid crystal composition are also required to have a larger negative dielectric anisotropy (Δ∈).
A compound having a high maximum temperature of a nematic phase (TNI) is expected in order to drive a liquid crystal display device in a wide temperature range.
In general, a liquid crystal compound has two or more ring structures. Almost all of the ring structures are six-membered rings such as a cyclohexane ring and a benzene ring. A liquid crystal compound having a five-membered ring such as a furan ring or a thiadiazole ring is also known, however, only a few examples have been reported on a liquid crystal compound having a cyclopentane ring or a tetrahydrofuran ring.
A liquid crystal compound having a cyclopentane ring where the dielectric anisotropy is small has been reported. See, for example, the patent document No. 1, the patent document No. 2, the non-patent document No. 1, the non-patent document No. 2 and the non-patent document No. 3. A liquid crystal compound having a small dielectric anisotropy is used to adjust physical properties such as viscosity, temperature range of a nematic phase, refractive index anisotropy or the like of the liquid crystal composition, and thus a compound having more excellent characteristics such as a property that further decreases the viscosity of the liquid crystal composition, for instance, is required.
A liquid crystal compound having a tetrahydrofuran ring where the dielectric anisotropy is small has been reported. See, for example, the patent document No. 3 and the non-patent document No. 4. The compound having a tetrahydrofuran ring is also required to have more excellent characteristics.
A compound having a cyano group at the terminal position is known as a liquid crystal compound having a cyclopentane ring or a tetrahydrofuran ring where the dielectric anisotropy is positive, and it is required that the compound can be utilized for a liquid crystal display having a TFT mode and have an excellent voltage holding ratio.
A compound having excellent characteristics is required, since a liquid crystal compound having negative dielectric anisotropy can be used for a VA mode-device or the like. However, a liquid crystal compound having a cyclopentane ring or a tetrahydrofuran ring where the dielectric anisotropy is negative is scarcely known.